How to reverse array key value order using array_reverse function in PHP

In PHP programming, array is a very commonly used data structure. Through the form of key-value pairs, we can easily access and process data. However, in some cases, we need to reverse the order of the array keys to achieve better data processing results. PHP provides a specialized function, the array_reverse function, which can easily reverse an array. Next, this article will introduce readers to how to use the array_reverse function in PHP to reverse the order of array key values.

1. Introduction to the array_reverse function

In PHP, the array_reverse function is a function used to reverse the order of an array. This function can operate on one-dimensional arrays, multi-dimensional arrays, and even associative arrays, and returns a new array in which the key values ​​of the original array will appear in reverse order. The function is defined as follows:

array array_reverse ( array $input [, bool $preserve_keys = FALSE ] )

Among them, the $input parameter is the array that needs to be reversed, and the $preserve_keys parameter is an optional parameter of Boolean type, used to specify whether to preserve the key name. When this parameter value is FALSE (the default), the key name will be reset. When this parameter value is TRUE, the key name will be retained.

2. Use the array_reverse function to reverse the array key value

Using the array_reverse function to reverse the array key value is very simple. You only need to define an array and pass it into the function as the $input parameter. That’s it. The following is a simple example:

<?php
$arr = array("apple", "banana", "orange", "grape");

print_r(array_reverse($arr));
?>

In the above code, we define an array $arr, containing 4 elements. We then reversed the array using the array_reverse function and output the result using the print_r function. Running the above code, you will get the following output:

Array
(
    [0] => grape
    [1] => orange
    [2] => banana
    [3] => apple
)

You can see that the key values ​​​​of the original array have been reversed and appear in the new array in reverse order.

3. Preserve the key names of the array

If you need to preserve the key names of the array, just set the $preserve_keys parameter to TRUE. The following is an example:

<?php
$arr = array("a" => "apple", "b" => "banana", "c" => "orange", "d" => "grape");

print_r(array_reverse($arr, true));
?>

In the above code, we define an associative array $arr, which contains 4 elements, each element has a key name (a, b, c, d). We then reversed the array using the array_reverse function, preserving the key names. Running the above code, you will get the following output:

Array
(
    [d] => grape
    [c] => orange
    [b] => banana
    [a] => apple
)

You can see that the key values ​​​​of the original array have been reversed, and the key names have also been retained.

4. Multi-dimensional array reversal

For multi-dimensional arrays, we can use a loop structure to reverse the sub-arrays one by one. The following is an example:

<?php
$arr = array(
    array("apple", "banana", "orange", "grape"),
    array("watermelon", "pineapple", "pear", "kiwi"),
    array("peach", "apricot", "cherry", "plum")
);

foreach ($arr as &$sub_array) {
    $sub_array = array_reverse($sub_array);
}

print_r($arr);
?>

In the above code, we define a three-dimensional array $arr, which contains 3 sub-arrays, each sub-array contains 4 elements. We then use a foreach loop statement to iterate through each sub-array and pass it as the $input parameter to the array_reverse function. Finally, we use the print_r function to output the reversed array. Running the above code, you will get the following output:

Array
(
    [0] => Array
        (
            [0] => grape
            [1] => orange
            [2] => banana
            [3] => apple
        )

    [1] => Array
        (
            [0] => kiwi
            [1] => pear
            [2] => pineapple
            [3] => watermelon
        )

    [2] => Array
        (
            [0] => plum
            [1] => cherry
            [2] => apricot
            [3] => peach
        )

)

As you can see, the key values ​​​​of each sub-array have been reversed and appear in the new sub-array in reverse order.

5. Summary

This article introduces how to use the array_reverse function in PHP to reverse the order of array key values. This function can be used to conveniently reverse arrays, and can be used in many situations such as one-dimensional arrays, multi-dimensional arrays, and associative arrays. To use, simply pass the array as a parameter to the function.

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